a) Field of the Invention
The present invention relates to a real image type vari-focal viewfinder for forming the image of air with rays which have not passed through a photographing lens and to be used in cameras equipped with photographing lenses capable of changing focal lengths thereof for focusing within broad ranges of object distances from infinite to very short distances.
b) Description of the Prior Art
The conventional real image type viewfinders adopts, as a means for helping photographers correct parallax, a fixed index indicating a photographing range for photographing objects located at short distances, or a visual field frame which is arranged at an intermediate image position and moved for photographing objects located at short distances.
The former type of conventional viewfinder is always visible, thereby constituting a hindrance to photographers when objects to be photographed are not located at short distances. Further, when the parallax is varied by zooming the photographic lenses, it is difficult to move the fixed index and the visual field frame in correspondence to the variation of the parallax.
As exemplified by the viewfinder disclosed by Japanese Patent Kokai Publication No. Hei 1-197727, there are known the viewfinders adapted so as to correct diopter and parallax at the same time by moving a lens which has an imaging function but no vari-focal function simultaneously in two directions along and perpendicular to the optical axis.
Due to the general requirement to enhance height of the effective rays on the intermediate imaging surface, it is obliged to prolong effective diameters of viewfinder optical systems while sacrificing compact designs of the viewfinders and it is difficult to correct aberrations in the optical systems. Further, since lens barrels are moved on the intermediate image surfaces, dust is floating within ranges where diopters are matched and adheres to lenses at high possibilities, thereby hindering clear sight of images within the visual fields.
The viewfinder disclosed by Japanese Patent Kokai Publication No. Hei 1-197727 is a real image type vari-focal viewfinder adapted so as to correct diopter and parallax by moving the lens which is kept fixed during variation of focal length, etc. This vari-focal viewfinder finder requires, in addition to the mechanism for varying focal length of the viewfinder, an interlocking mechanism for moving a lens other than the lens moved for variation of focal length, thereby having a very complicated structure and requiring a high manufacturing cost.